A floating tone is a morpheme[1] or element of a morpheme that contains no consonants, no vowels, but only tone. It cannot be pronounced by itself, but affects the tones of neighboring morphemes.[2][3]

An example occurs in Bambara. Bambara has two phonemic tones,[4]high and low. In this language, the definite article is a floating low tone. With a noun in isolation, it is associated with the preceding vowel, turning a high tone into a falling tone: [bá] river; [bâ] the river. When it occurs between two high tones, it downsteps the following tone:

[bá tɛ́]it's not a river

[bá tɛ̄] (or [bá ꜜ tɛ́]) it's not the river

Also common are floating tones associated with a segmental morpheme such as an affix.[5] For example, in Okphela, an Edoid language of Nigeria,[6] the main negative morpheme is distinguished from the present tense morpheme by tone; the present tense morpheme (á-) carries high tone, whereas the negative past morpheme (´a-) imposes a high tone on the syllable which precedes it:

oh á-nga he is climbing

óh a-nga he didn't climb

Floating tones derive historically from morphemes which assimilate[7] or lenite[8] to the point where only their tone remains.[9]

↑Zimmerman, 1. 1858. A grammatical sketch and vocabulary of the Akra- or Galanguage with an appendix on the Adanme dialect. Stuttgart, 2 vols. Republished with an Introduction by 1. Berry, Gregg International, 1972.